Transverse fracture in laminated fiber-reinforced brittle matrix composites

Abstract

Cracking during uniaxial tensile loading of laminated fiber-reinforced composites usually begins in the 90° layer (with fibers normal to the axis of loading). When such transverse cracks in the 90° ply reach the 0° ply, they are arrested by the fibers in the 0° ply so that the transverse crack growth is restricted in the 90° ply. Such crack growth eventually leads to extensive cracking of the 90° ply. The critical applied stress for the propagation of these transverse cracks in the 90° layers, which is referred to as the cracking stress, is obtained based on a distributed spring model which simulates the constraining effect provided by the intact 0° layers to transverse cracks in the 90° layers. First, the spring stress—stretch relation is derived analytically based on a modified shear-lag model and its accuracy is verified using a boundary element method calculation. The spring stress—stretch relation takes into account the interface behavior that frictional slip can occur at the ply interfaces. The cracking stress, which is dependent on the crack length in the 90° ply, is evaluated based on the bridging spring stress—stretch relation. For cracks with lengths much larger than the ply thickness, the steady-state cracking stress is obtained in closed form. For shorter cracks, the cracking stress is obtained by solving an integral equation. Finally, the theoretical results for long cracks are compared with experimental data for a laminated SiC fiber, calcium—alumino-silicate (CAS) glass matrix composite.